1. Field of the Invention
The invention relates to charged particle beam microscopes and, particularly, to arrangements for equipping such a microscope with a minicolumn.
2. Discussion of Related Art
Charged particle beam microscopes, such as an electron microscope, are well known in the art, and are widely used during the manufacture of semiconductor wafers. For ease of discussion, the remaining disclosure makes reference to electrons as the charged particles; however, it should be appreciated that the discussion is equally applicable to other charged particles. The elements of a conventional electron microscope which are of particular relevance here are depicted in FIG. 1. Specifically, a vacuum chamber 10 houses an x-y stage 20 upon which the wafer 40 is placed by a robot (not shown). The chamber 10 is evacuated via outlet 70. The wafer 40 is introduced into the chamber 10 via a load lock 30 so as to avoid having to evacuate the chamber 10 each time a wafer is loaded.
An electron column 50 is hermetically attached to the chamber 10. The column 50 houses the electron source and all the necessary electron optics (not shown). The column 50 is evacuated via outlet 60. The diameter of a conventional column is roughly 6-10 inches, while its height is roughly 15-30 inches. The conventional column is capable of providing an electron beam of sufficiently small diameter for wafer and reticle inspection, review and metrology.
One disadvantage of the prior art design is that whenever the column requires a repair which necessitates its removal from the chamber or breaking the vacuum in the column, the vacuum of the chamber is also broken. Breaking the vacuum in the chamber necessarily means that the microscope will be out of service for several hours. Another disadvantage is the requirement for separate vacuum systems for the column and the chamber, which increases the complexity and price of the system, while adversely affecting its reliability and stability.
Recently, a new type of column has been developed, and is generally referred to as a xe2x80x9cminicolumn.xe2x80x9d A cross section of a minicolumn investigated by the current inventors is depicted in FIG. 2. In FIG. 2, element 200 is the electron source (preferably a Schottky emitter), 210 is an aperture (suppressor), and 220 generally designates the lens arrangement. More specifically, lens arrangement 220 comprises three lenses 230 made of a conductive material and insulating spacers 240 interposed between the lenses 230. Ordered from the emitter, the lenses 230 comprise an extraction lens, a focusing lens, and an acceleration lens, respectively.
Notably, the diameter and height of such a column is measured in single-digit centimeters. More specifically, the diameter of the lens arrangement depicted in FIG. 2 is on the order of 3 centimeters, while its height is on the order of 1 centimeter. While this column is remarkably smaller than the conventional column, it provides an electron beam which has small diameter and was determined by the present inventors to be suitable for use in electron microscopes. Further information regarding the study of the minicolumn is presented in F. Burstert, D. Winkler and B. Lischke, Microelectronic Engineering 31 (1996) 95; and in Miniature Electrostatic Lens for Generation of a Low-Voltage High Current Electron Probe, C. D. Bubeck, A.; Fleischmann, G. Knell, R. Y. Lutsch, E. Plies and D. Winkler, Proceedings of the. Charged Particle Optics Conference, Apr. 14-17, 1998.
Accordingly, the present invention provides arrangements for installing minicolumns onto a charged particle microscope, especially electron microscopes, to while providing synergistic advantages over the prior art column arrangement. That is, the disclosed arrangements provide advantages in addition to the advantages of the minicolumn per se.
According to one set of embodiments of the invention, a second load lock is provided on the microscopes vacuum chamber. The second load lock is used to introduce the minicolumn into the chamber without having to break the vacuum in the chamber. Thus, a technician can replace the minicolumn without having to break the vacuum in the chamber.
According to another set of embodiments, the minicolumn is situated inside the microscope""s vacuum chamber. While this arrangement necessitates breaking the vacuum for each minicolumn service, is still advantageous in that here is no need for separate vacuum system for the column. This is advantageous especially if more than one minicolumn is used inside the chamber.
Another advantage of the invention is that it provides arrangements for more than one minicolumn per microscope. This arrangement is especially advantageous for taking multiple perspectives simultaneously or for increasing the throughput.